I am trying, as a complete novice, to see if I could use Linux. I wish to trial it using what I think is called a 'live' disc. I downloaded from the web site and burned a CD, but when I tried to boot from it,after the intial screen for Ubuntu Mint, it changed to a black screen displaying the following "Loading. Invalid or corrupt kernal image--boot " What am I doing wrong and how should I proceed.

It sounds as though there is a problem with your CD. Firstly check that the MD5 sum of your download is the same as the file on the download site, then burn the CD at the slowest speed possible. This should ensure a good copy. If you still do not succeed in being able to boot the CD then it may be that you do not have enough RAM on your machine.